Awesome moment set back a French intellectual (10)
I believe the answer is:
monumental
'awesome' is the definition.
(thesaurus)
'moment set back a french intellectual' is the wordplay.
'moment' becomes 'mo' (slang abbreviation. e.g. 'just a mo').
'set back' is a reversal indicator.
'a french' becomes 'un' ('a' in French).
'intellectual' becomes 'mental' ('mental' can be similar in meaning to 'intellectual'**).
'un' in reverse letter order is 'nu'.
'mo'+'nu'+'mental'='MONUMENTAL'
(Other definitions for monumental that I've seen before include "Great in importance" , "Stupendous" , "Enormous" , "Massive and lasting" , "Large and important" .)